Microwave pasteurization improves food safety, flavor

PULLMAN, Wash. – A new technology available to food companies increases product quality while reducing the chance of contaminated chilled or frozen meals being sold in retail markets.

A group of engineers led by Juming Tang, distinguished chair of food engineering and associate chair of biological systems engineering at Washington State University, has developed a novel microwave-assisted pasteurization system that can semi-continuously process 8- to 20-oz. pre-packaged chilled meals. This marks an important milestone in a research program funded by a $5 million U.S. Department of Agriculture (USDA) National Institute of Food and Agriculture (NIFA) grant awarded in 2011 to WSU and partners across the country.

A pilot-scale microwave-assisted pasteurization system developed at Washington State University.

WSU has established “pilot-scale capacity” whereby Tang and his colleagues can work with food companies to adapt the technology to a producer’s needs and then manufacture production equipment via a third party, making the system “scalable for industrial production,” said Tang. WSU anticipates licensing this technology to its start-up, Food Chain Safety, for commercialization in the coming months.

According to Tang, the 915 MHz microwave-assisted pasteurization process significantly improves upon traditional thermal pasteurization, offering food producers a more efficient means of making foods safe while retaining consumer appeal. After two to four minutes of heating the product to 194 F/90 C, which is below the boiling point of water, the numbers of pathogenic bacteria can be reduced a million-fold.

“We can control foodborne pathogens and viruses and provide high-quality products,” said Tang. The process also allows traditionally frozen meals to be refrigerated instead of frozen, saving retailers and consumers significant energy costs.

“We had some exciting early results. The quality of microwave pasteurized foods – specifically mollusks, shrimp and tofu – is substantially better than conventionally pasteurized foods,” said Barbara Rasco, professor in WSU’s School of Food Science and collaborator on the project. A shelf life exceeding one month at refrigeration temperatures has been achieved for several formulated food items, including stroganoffs, curries, burritos and hors d’oeuvres.

Shyam Sablani, another WSU collaborator, is leading package development.

Pasteurizing chilled meals using the new method preserves product quality more than commercial canning (sterilization) processes for shelf-stable foods. Traditional canning typically operates at 249 F/120 C or higher in order to kill the dangerous pathogen Clostridium botulinum; but the temperature, pressure and length of the canning process often degrades food quality, making it less acceptable to consumers, said Tang.

The technology developed by his laboratory may help fulfill the mandate of the federal 2011 Food Safety Modernization Act, which requires food producers nationwide to add steps in food production operations to make sure products are safe, Tang said.

“This new technology is an excellent example of the type of innovation NIFA seeks to deploy across the nation to keep our food supply safe for all consumers,” said Sonny Ramaswamy, NIFA director. “Food safety is a critical priority for USDA, and I applaud Washington State University’s efforts to address this challenge with ground-breaking research that will be useful for food processors testing the safety and quality of their products.”

Other institutions involved with the project include the University of Tennessee, North Carolina State University, the U.S. Army Soldier Systems Center and USDA-Agricultural Research Service Eastern Regional Research Center. More information on the people and organizations involved can be found at http://microwavepasteurization.wsu.edu/mwp-main/people.html.